title: Prevalence and persistence of Salmonella in cohorts of feedlot cattle.
abstract: Our objectives were to determine factors associated with fecal prevalence of Salmonella at feedlot entry and within 24 h of harvest (preharvest), and to assess potential persistence of Salmonella strains within cattle populations. This repeated cross-sectional study followed 5559 beef cattle within 30 feedlot cohorts. Samples (n = 30) of fresh feces were collected from the pen floor of each cohort at feedlot entry and preharvest. Samples were subjected to a selective Salmonella isolation protocol and serotypes were determined for Salmonella isolates. Genetic similarity of a subset of isolates was determined using pulsed-field gel electrophoresis (PFGE). Cattle health and performance data were recorded electronically by feedlot personnel. Cohort-level generalized linear mixed models were used to assess bivariable associations. Fecal prevalence of Salmonella within a cohort at feedlot entry (mean = 64.7%) was not associated with preharvest prevalence (mean = 72.6%). Prevalence at feedlot entry was negatively associated with mean entry weight (p = 0.02). Preharvest prevalence was positively associated with the number of days in the feedlot (p = 0.02), cumulative morbidity (p = 0.01), and cumulative mortality (p = 0.03). We recovered Salmonella isolates with identical PFGE profiles both at feedlot entry and preharvest from 14 cohorts of cattle. Fecal prevalence of Salmonella immediately before harvest may be higher in subsets of the feedlot population, but does not appear to be affected by prevalence at feedlot entry. However, PFGE subtypes of Salmonella appear to persist within and among feedlot cohorts throughout the feeding period.
authors.affiliation: Department of Diagnostic Medicine/Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, Kansas 66506-5705, USA.
authors.forename: Charles C
authors.initials: CC
authors.lastname: Dodd
authors.forename: David G
authors.initials: DG
authors.lastname: Renter
authors.forename: Xiaorong
authors.initials: X
authors.lastname: Shi
authors.forename: M Jahangir
authors.initials: MJ
authors.lastname: Alam
authors.forename: T G
authors.initials: TG
authors.lastname: Nagaraja
authors.forename: Michael W
authors.initials: MW
authors.lastname: Sanderson
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology* / Q000382:microbiology; D015331:Cohort Studies; D003430:Cross-Sectional Studies; D016521:Electrophoresis, Gel, Pulsed-Field / Q000379:methods / Q000662:veterinary; D005243:Feces / Q000382:microbiology*; D005260:Female; D005430:Floors and Floorcoverings; D008297:Male; D015995:Prevalence; D012475:Salmonella / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*; D012481:Salmonella Infections, Animal / Q000453:epidemiology* / Q000382:microbiology; D012703:Serotyping / Q000662:veterinary; D013781:Texas / Q000453:epidemiology; D013997:Time Factors